It is known in the field of indirect injection (prechamber type) diesel engines to provide a relatively high compression ratio of around 20 or 22 to 1 in order to assure proper starting and running of the engine, especially under cold operating conditions. A glow plug, which is commonly electrically heated, is usually provided to assist vaporization of fuel for starting when the engine is cold.
It is also known to provide for exhaust gas recirculation in order to limit the formation of oxides of nitrogen in the high temperature combustion process of the diesel engine. Such recirculation is generally provided by conducting exhaust gases from the engine exhaust system into the induction system, for example at the intake manifold.
It is further believed that the relatively higher compression ratios of prechamber diesel engines encourage the formation of nitrogen oxides and particulates as well as causing higher friction losses as compared to engines operating at lower compression ratios.